BACKGROUND: Balloon sinus dilation (BSD) is an increasingly used tool in endoscopic sinus surgery (ESS). The tissue-sparing nature of the instrumentation allows for properly selected patients to undergo office-based procedures under local anesthesia. METHODS: This was an Institutional Review Board (IRB)-approved, prospective, 14-center trial. Patients (n = 203) requiring ESS for medically refractory chronic sinusitis underwent transnasal BSD treatment in an office setting under local anesthesia. Safety, tolerability, technical success, clinical efficacy (20-item Sino-Nasal Outcome Test [SNOT-20]), and radiographic outcome (Lund-Mackay [LMK] score) of ESS with BSD in the office setting were assessed. Subjects were followed at 2, 8, and 24 weeks. RESULTS: A total of 552 sinuses were dilated in 203 patients: 47.6% maxillaries, 45.5% frontals, and 6.9% sphenoids. Seventy-seven patients were revisions of prior ESS. The mean number of sinuses dilated per subject was 2.7. Technical dilation success was 93.3%, 90.5%, and 93.7% for maxillary, sphenoid, and frontal sinuses, respectively. SNOT-20 and LMK computed tomography (CT) scoring showed statistically significant improvement at 24 weeks (p < 0.0001) and clinically significant improvement in quality of life. The procedure was reported as tolerable or highly tolerable by 82.3% of patients. There were 0.15 postoperative debridements per patient and the majority returned to normal activity within 48 hours. One (0.5%) procedure-related adverse event related to periorbital swelling was reported, which spontaneously resolved shortly after the procedure without further sequelae. CONCLUSION: Performance of ESS with BSD in the office under local anesthesia is feasible, well-tolerated, safe, and effective. Twenty-four week follow-up demonstrates clinical and statistical improvement in patient quality of life and radiographic outcomes.